flat containers prototype

components/omnibox/browser/url_index_private_data.cc

Index: components/omnibox/browser/url_index_private_data.cc
diff --git a/components/omnibox/browser/url_index_private_data.cc b/components/omnibox/browser/url_index_private_data.cc
index 6ca56db8c245fcce787c720aeaa98eb36e788d4b..6caab4b391cc55bfb73f005f85a0d4ad01efc68c 100644
--- a/components/omnibox/browser/url_index_private_data.cc
+++ b/components/omnibox/browser/url_index_private_data.cc
@@ -278,7 +278,7 @@ ScoredHistoryMatches URLIndexPrivateData::HistoryItemsForTerms(
     for (SearchTermCacheMap::iterator cache_iter = search_term_cache_.begin();
          cache_iter != search_term_cache_.end(); ) {
       if (!cache_iter->second.used_)
-        search_term_cache_.erase(cache_iter++);
+        cache_iter = search_term_cache_.erase(cache_iter);
       else
         ++cache_iter;
     }
@@ -630,7 +630,7 @@ HistoryIDSet URLIndexPrivateData::HistoryIDsForTerm(
     for (WordIDSet::iterator word_set_iter = word_id_set.begin();
          word_set_iter != word_id_set.end(); ) {
       if (word_list_[*word_set_iter].find(term) == base::string16::npos)
-        word_id_set.erase(word_set_iter++);
+        word_set_iter = word_id_set.erase(word_set_iter);
       else
         ++word_set_iter;
     }
@@ -642,14 +642,15 @@ HistoryIDSet URLIndexPrivateData::HistoryIDsForTerm(
   // the sets from each word.
   HistoryIDSet history_id_set;
   if (!word_id_set.empty()) {
+    auto unsafe = history_id_set.unsafe_access();

[dyaroshev, 2016/09/13 12:28:13]

Here is the tight spot I was talking about in chromium-dev. Without using unsafe
access here, I've seen conditions where flat was outperformed by std::sets/maps.

     for (WordIDSet::iterator word_id_iter = word_id_set.begin();
          word_id_iter != word_id_set.end(); ++word_id_iter) {
       WordID word_id = *word_id_iter;
       WordIDHistoryMap::iterator word_iter = word_id_history_map_.find(word_id);
       if (word_iter != word_id_history_map_.end()) {
         HistoryIDSet& word_history_id_set(word_iter->second);
-        history_id_set.insert(word_history_id_set.begin(),
-                              word_history_id_set.end());
+        unsafe->insert(unsafe->end(), word_history_id_set.begin(),
+                       word_history_id_set.end());
       }
     }
   }